This invention relates to a dilution control system that utilizes closed-loop adaptive control based on real-time engine work output to increase engine efficiencies and reduce emissions.
Control of internal combustion engines is currently premised on the reading of various engine operating parameters such as engine speed, intake manifold pressure, coolant temperature, throttle position, and exhaust oxygen concentration. These parameters are used in conjunction with specific, predetermined base maps calibrated by a baseline engine to select the ignition timing, fuel injector duration, and exhaust gas recirculation ("EGR") of the engine so that the engine achieves maximum efficiency and minimum emissions as determined by the baseline engine.
Base map control is simple and can be very effective for new engines. This control, however, has drawbacks as the engine ages and deposits build up in the combustion chambers and on the valves. More importantly, with emissions standards now requiring an automobile to remain within strict emissions limits for at least the first 100,000 miles, base map control cannot maintain the engine at or near its maximum efficiency and minimum emissions operating point for the required mileage.
Many experimental engine control systems use base map control to vary fuel-air mixture dilution, which reduces emissions. However, due to the complexities of running an engine heavily diluted, these control systems are not capable of maintaining maximum efficiency. For this reason, these systems often sacrifice maximum efficiency to maintain the low emissions required for at least the first 100,000 miles.
The current strict emissions standards require engine control systems to improve engine efficiencies of internal combustion engines. Research indicates that to increase such efficiencies, internal combustion engines must operate with a fuel-air mixture heavily diluted with excess air, exhaust gases, or a combination of both. This produces more efficient combustion, while also reducing pumping losses at part throttle conditions. The current strict emissions standards also require that internal combustion engines meet the emissions criteria for at least the first 100,000 miles. Therefore, an engine control system adaptable to changing engine conditions over the life of the engine is needed so that the engine can operate at maximum efficiency and minimum emissions for at least the first 100,000 miles.
Present engine control systems, and more specifically, dilution control systems, do not adequately control internal combustion engines so that maximum efficiency and reduced emissions are achieved for the required mileage. For example, U.S. Pat. No. 4,543,934 provides a fuel-air mixture dilution control system by monitoring cycle-to-cycle fluctuations of the angular position of peak combustion pressure of each engine cylinder. This control system determines an air/fuel ratio at which engine stability changes between stable and unstable conditions. A controller attempts to continuously operate the engine at the engine stability point, leaning the fuel-air mixture until the engine becomes unstable, and enriching the fuel-air mixture until the engine becomes stable again. This stability point is often beyond the point of maximum efficiency and is often also beyond the point of minimum emissions.
Other control systems, such as the system disclosed in U.S. Pat. No. 4,736,724, control the air/fuel ratio by measuring the burn duration of each engine cylinder. The duration is compared to an adaptive engine map that determines the lean limit for the engine at a specific speed and load. The engine is then controlled to operate at the most dilute point possible for a desired engine stability, but this point is often beyond the point of maximum efficiency, and is often beyond the point of minimum emissions.
U.S. Pat. No. 4,621,603 discloses three different methods of controlling the level of fuel-air mixture dilution using pressure ratio management. The first system controls the amount of diluent at a specified value as a function of engine speed and load. The second system controls the amount of diluent to adjust the burn rate or combustion time. The third system controls the amount of diluent using cycle-to-cycle variability as both a method to balance fuel delivery to each combustion chamber, and as a method of stability control. Pressure ratio management allows for a simplified algorithm, but does not supply the engine controller with enough information for complete engine control because taking pressure readings only at specific points allows the controller only to estimate engine stability, and therefore, this system suffers the same limitations of the previously mentioned systems.
Alternatively, the system of U.S. Pat. No. 4,621,603 could be used at a specific air/fuel ratio that is calculated according to base maps, but even with an adaptive algorithm, the pressure ratio does not give enough information to allow the system to provide both maximum efficiency and minimum emissions for at least the first 100,000 miles. The system in U.S. Pat. No. 4,621,603, for example, would have extreme difficulty calculating the engine mean effective pressure if spark timing varies by large amounts. Such a calculation is necessary for an engine to achieve maximum efficiency at highly dilute mixtures and minimum emissions for at least the first 100,000 miles.